Low temperature cure coating compositions based on amine-reactive polymers are illustrated in Cady et al., U.S. Pat. No. 4,446,280, in European Patent Office (EPO) Application No. 0138025, dated Apr. 24, 1985, and EPO Application No. 0020000, dated Dec. 10, 1980. These coating compositions are based upon solvent borne, solution polymers containing activated ester groups. In U.S. Pat. No. 4,446,280, the polymer thereof is crosslinked by the use of an amine-terminated triazine resin, to give a film with good resistance properties. In EPO Application No. 0138025, a superior crosslinker is described, and this is, preferably, a triamine made by condensing a maleate ester and an alkylene diamine.
The use of such a crosslinker makes possible good low temperature cure, while yielding a hard yet flexible films having good resistance properties, and provides efficient utilization of the amine-reactive groups of the crosslinkable polymer. Hence, the provision of such a crosslinking agent and of compositions based thereon useful, for example, for coatings and adhesive applications, has constituted a significant advance in the art.
However, such compositions and coatings do have one drawback and that is a slight deficiency in their resistance to corrosive environments, as demonstrated for example, on exposure to sprays of hot salt solutions. It would be desirable to provide such compositions with corrosion resistance approaching that of epoxy resins and such has now been accomplished. The combinations of this invention employing benzotriazole or a polypyridyl, alone, or in further combination with 2-hydroxypyridine vastly improve the corrosion resistance of the state of the art systems.